Wave energy apparatus

ABSTRACT

Wave energy apparatus comprises a hollow buoy (2) for floating in water. The buoy has a turbine (5) which rotates in response to air flow into and out of the buoy (2) through a nozzle (4). The turbine (5) is designed to rotate in the same direction regardless of the axial direction of air flow. The air flow is caused by the change of level of water (W) within the buoy in response to wave motion. 
     To enable rocking motion to be accommodated as well as vertical motion, the interior of the buoy is divided into a plurality of conduits (9), by means of partitions (6), the conduits directing air to different portions of the turbine (5). The conduits (9) preferably have lateral openings (10) and may be defined in part by upwardly inclined portions (11) of an inertial body (8). 
     In an alternative embodiment the buoy has a closed bottom and liquid in the buoy is acted on by a centrally disposed air spring.

This invention relates to wave energy apparatus, that is apparatusadapted to convert the energy of waves produced on the surface of thesea or other bodies of water, into a useful form such as electricalenergy, hydraulic energy and so forth.

Wave energy apparatus is known, in which the displacement of watercauses air or another fluid to flow through a turbine which drives anelectrical generator. Since the water displacement is oscillatory innature, the turbine may advantageously be such that the flow of air ineither direction will cause the turbine rotor to rotate in a singledirection. The apparatus may be in the form of a floating buoy or thelike.

U.S. Pat. No. 3,064,137 discloses a buoy having a vertically extendingopen ended passage. Water can enter the passage at the lower end, andoscillation of the water level inside the passage causes air to flowalternately in and out of the upper end of the passage. Adjacent theupper end of the passage is positioned a turbine with a rotor having twosets of blades which respectively operate in opposite directions of airflow, so that the rotor always rotates in the same direction.

In U.S. Pat. No. 4,221,538 there is disclosed an improved form ofturbine incorporated in wave energy apparatus. The rotor has a pluralityof blades each of which is of aerofoil cross-section and is fixed withits plane of zero lift normal to the axis of the rotor. This causes therotor to rotate in a single direction, regardless of the direction ofair flow. The apparatus is once again in the form of a buoy, having anopen bottom so that an oscillating body of water within the buoy causesthe air flow.

As is described in U.S. Pat. No. 3,064,137, the movement of a buoy canbe resolved into two basic modes: vertical movement caused by the riseand fall, or heave, of the waves, and rocking movement. The verticalmovement has been considered the most important source of energy inapparatus in this type, and the apparatus of U.S. Pat. Nos. 3,064,137 or4,221,538 is capable only of absorbing energy in this mode, from thevertical oscillation of a body of water.

It has now been found that the absorption of roll or pitch energy couldconsiderably increase the efficiency of wave energy apparatus of thetype described above. Calculations have shown that a buoy forexample--which can be considered as a quasi-spherical body--absorbs waveenergy efficiently when undergoing orbital motion, that is a combinationof vertical and horizontal movement. Horizontal movement is manifestedas roll or pitch of the buoy.

In wave energy apparatus as described previously, the water contained bythe buoy can be considered as a driving liquid, for pumping air, whichcan be considered as a working fluid, through the turbine in eitherdirection. Pumping is achieved only by vertical oscillation of the bodyof driving liquid.

As a result of roll or pitch of the buoy, there will be differentialdisplacement of driving liquid in different parts of the buoy. An objectof the invention therefore is to enable the absorption of energy frompitch or roll by utilising such differential displacement as anadditional pumping source.

According to the invention there is provided wave energy apparatuscomprising a body adapted to float in water, said body being providedwith a turbine having a rotor such that a flow of working fluid throughthe turbine in either axial direction causes the rotor to rotate alwaysin the same direction, and a plurality of conduits for directing workingfluid to respective regions of said turbine for axial flow therethrough,each of said conduits being connected to a source of driving liquid atdifferent respective locations in said body, the arrangements being suchthat the driving liquid urges working fluid along the conduits inresponse to both vertical and rocking movements of the body.

Considering vertical movement only, the conduits will generally supplyworking fluid to the turbine in phase as regards flow direction. Inresponse to rocking movement, the flow direction for any given conduitwill depend on the position of the driving fluid to which it isconnected, relative to the rocking axis. Since the rotor rotates in thesame direction regardless of the flow direction of the working fluid,rocking movement will result in the rotor being driven.

To modify the apparatus of for example U.S. Pat. No. 4,221,538 at leastone partition may be provided inside the buoy, extending from the regionof the turbine into the water. Without such a partition, whilst rockingmotion would produce, in the water inside the buoy, an increase in levelon one side of the rocking axis and a corresponding decrease in level onthe other side of the rocking axis, there would be no net flow of airthrough any part of the turbine. By providing the partition, there willbe a flow of air up through one region of the turbine, and down throughanother region of the turbine. As a rotor blade passes from one regionto the other, it will encounter a change in the direction of air flowbut will continue to drive the rotor in the same direction.

Two conduits, provided for example by a single partition extendingdiametrically across the column of water contained in the buoy, wouldpermit the absorption of rocking energy only about a single axisextending across the buoy in the plane of the partition. This might beof use if the wave direction is constant and the buoy is moored so as tobe suitably aligned. Preferably however, at least three conduits areprovided equi-angularly spaced. These could be formed by three radiallyextending partitions within the buoy. Four, six, eight or more conduitscould be employed if required.

The rocking movements of the body are produced by horizontal componentsof wave movement. For these to be effectively converted into pitch orroll of the body, the rigid contents of the body should have a lowcentre of mass. A body suitably constructed, and with at least threeconduits, should be able to absorb energy in five modes, namely heave,pitch, surge, sway and roll.

Preferably, in use the body should be substantially immersed if the bestuse is to be made of horizontal components of oscillation; the wettedsurface should be maximised in order to receive the maximum horizontalforces, but the velocity ratio will be increased for unnecessarily deepimmersion. The body should preferably be rotationally symmetric aboutthe vertical axis.

In the wave energy apparatus of U.S. Pat. No. 4,221,538 the floatingbody is ballasted by means of a submerged, water-filled sphere. It hasnow been found that this sphere could be a source of energy losses,since it acts as an uncontrolled radiator. Preferably therefore theballast is in the form of a dense solid mass at the base of the body.The resultant low centre of mass improves the absorption of horizontalcomponents of wave movement, and means that the centre of roll will benear the base of the body, so that large cyclic mooring forces can beobviated. The mooring points are preferably situated near the base ofthe body.

In the wave energy apparatus disclosed in U.S. Pat. Nos. 3,164,137 or4,221,538, the buoy has an open bottom, and the oscillating column ofwater is provided by a portion of the sea surrounded by the buoy. Thenecessary oscillatory pumping action can however be provided by a bodyof driving liquid contained within a closed-bottom buoy, providing thatthe driving liquid is acted upon by a resilient medium so that thenecessary oscillation is obtained in response to vertical wavemovements. The resilient medium could be in the form of an air spring,which may be defined by an air trap in the form of a hollow body with anopen bottom and closed top.

Since the liquid at the centre of the floating body cannot provide muchresponse to roll, the air spring could be provided in this region.Advantageously a single body of driving liquid, such as water, is usedinside the body, and a single air spring arrangement. If desired,however, separate supplies of liquid with independent air springs, couldbe used for separate conduits directing air to the turbine. Heavyballast such as concrete for example, may be required to compensate forthe buoyancy of the entrapped air.

The buoy could be filled with sea water to the appropriate level, or befilled with any other suitable liquid such as fresh water or waste.

In the above described arrangement the buoy could be enclosed at thetop, although the volume of air space above the liquid in the conduitswould require to be much greater than the air entrapped, perhaps beingten times as great. Such a system of total enclosure would protect theturbine and the interior of the buoy. The buoy could be easilyconstructed to be strong and would be unsinkable.

Two embodiments of the invention will now be described by way of exampleand with reference to the accompanying drawings, in which:

FIG. 1 is a vertical section through a first embodiment of apparatus inaccordance with the invention;

FIG. 2 is a horizontal section on the line II--II of FIG. 1;

FIG. 3 is a horizontal section of the line III--III of FIG. 1;

FIG. 4 is a horizontal section on the line IV--IV of FIG. 1;

FIG. 5 is a vertical section through a second embodiment of apparatus inaccordance with the invention;

FIG. 6 is a horizontal section on the line VI--VI of FIG. 5;

FIG. 7 is a horizontal section on the line VII--VII of FIG. 5; and

FIG. 8 is a horizontal section on the line VIII--VIII of FIG. 5.

Referring now to the drawings, in FIG. 1 there is shown wave energyapparatus in accordance with the invention, this particular embodimentbeing a modification of the type of apparatus disclosed in U.S. Pat. No.4,221,538.

The apparatus comprises a buoy 1 including an open bottomed canopy 2.Around the periphery of the canopy 2 is an annular buoyancy chamber 3.The top of the canopy 2 is provided with an opening in the form of aconvergent-divergent nozzle 4. In the nozzle 4 is mounted a turbine 5connected to a generator (not shown). The turbine is of the type with arotor which always rotates in the same direction, regardless of thedirection of flow. The turbine is preferably of the type disclosed inU.S. Pat. No. 4,221,538. It could comprise a plurality of rotors on acommon shaft. It could alternatively include an even number of coaxiallydisposed rotors on separate shafts which alternatively rotate inopposite directions.

The interior of the canopy is divided into three sections by radiallyextending partitions 6, equi-angularly spaced. The partitions extendfrom the wall of the canopy to a central supporting column 7. At thebottom of the column 7 is provided an inertial body in the form of avessel 8 having a toroidal form at its lower end. This vessel can beflooded with water, to provide a low centre of mass for the buoy, sothat it can pitch and roll freely.

The partitions 6 extend from above the turbine 5, to below the waterlevel W, and are attached at their lower ends to vessel 8. This providesa strong structure.

The partitions 6 divide the interior of the buoy into three separateconduits 9 for directing air to the turbine 5. Each conduit 9 is open atthe bottom through an opening 10 defined between the canopy 2 and theupper, upwardly inclined conical surface 11 of vessel 8. In response tothe heave motion, the water in the three conduits will oscillate,vertically, rising and falling simultaneously in the three conduits.Pitching or rolling will cause the water to rise in one or more of theconduits, and to fall in the remainder. Thus air will be forced upwardsthrough the one or more conduits, and drawn into the remainder. Theresultant air flows, although in different directions, will cause therotor of the turbine 5 to rotate. Thus, both heave and pitch or rollenergy can be harnessed.

As can be seen, the openings 10 of vertical conduits 9 are laterallydisposed. It has been found that the ability of the device to acceptenergy from a wide range of waves can be improved by careful design ofthe geometry of the conduit entrance. A lateral facing conduit entranceprovides an advantage in that the interior conduit wall serves totranslate wave particle motions in the horizontal plane to motion in thevertical plane by reflection against e.g. the inclined conical surface11. The horizontal components can thus be better utilised. It has beenproposed that a more upwardly facing conduit, e.g. of J-shapedlongitudinal section, would be useful.

The apparatus shown in FIGS. 5 to 8 comprises a buoy 12 in the form of aquasi-spherical, open topped flask. The opening is in the form of aconvergent-divergent nozzle 13. In the nozzle 13 is a turbine 14 of thetype described in relation to the previous embodiment. The buoy isprovided at its base with heavy ballast 15, for example of concrete.Mooring points 16 are provided at the base of the buoy. In this matter,horizontal movements are converted into pitch or roll about a centrenear the base, this reducing cyclic mooring forces.

Within the buoy are provided three radial partitions 17 and an annularconical partition 18. These define three conduits for directing airthrough the turbine 14, the radial partitions extending up into thenozzle 13 of the buoy. The annular partition defines a conicalopen-bottomed chamber. When the buoy is filled with sea-water--oranother liquid--up to the level W, air is trapped in space 19 bounded bythe partition 18.

When the buoy undergoes heave motion, the liquid within oscillatesagainst the resilient action of the entrapped air, so that air passesthrough the turbine. Pitching or rolling will cause liquid to rise andfall in different conduits defined by the partitions, in a manneranalogous to that of the previous embodiments.

The embodiments of wave energy apparatus described herein can be ofrelatively large size, for example their diameter being 80% of thewavelength to be experienced--such wavelengths being for example of theorder of 100 m. Large size buoys would be particularly useful forgeneral energy generation; smaller buoys can be used for specialpurposes.

I claim:
 1. Wave energy apparatus comprising a body adapted to float inwater, said body being provided with a turbine such that a flow ofworking fluid through the turbine in either axial direction causes therotor to rotate always in the same direction, and a plurality ofconduits for directing working fluid to respective regions of saidturbine for axial flow therethrough, each of said conduits beingconnected to a source of driving liquid at different respectivelocations in said body, the arrangement being such that the drivingliquid urges working fluid along the conduits in response to bothvertical and rocking movements of the body.
 2. Apparatus as claimed inclaim 1, wherein the conduits are vertically disposed.
 3. Apparatus asclaimed in claim 2, wherein the conduits are defined by at least onevertically extending partition inside a hollow buoy.
 4. Apparatus asclaimed in claim 3, wherein the body has openings for communicating thelower ends of the conduits with water in which the body is to float,such water constituting the said driving liquid.
 5. Apparatus as claimedin claim 4, wherein the openings are laterally disposed.
 6. Apparatus asclaimed in claim 5, wherein the bottom of each conduit is defined by aportion inclined upwardly with respect to the base of the respectiveopening.
 7. Apparatus as claimed in claim 4, 5 or 6, comprising a canopyhaving an open top and an open bottom, and an inertial body beneath thecanopy and connected thereof.
 8. Apparatus as claimed in claim 3,wherein the body has a closed bottom and is adapted to contain a body ofsaid driving liquid, means being arranged to provide a resilient mediumfor acting against the driving liquid.
 9. Apparatus as claimed in claims2, 3, 4, 5, 6 or 8 wherein the body is rotationally symmetrical aboutits vertical axis and wherein at least three equiangularly arrangedconduits are provided.
 10. Apparatus as claimed in claims 1, 2, 3, 4, 5,6 or 8 wherein the turbine comprises a rotor having a plurality ofblades each of which is of aerofoil cross-section and is fixed with itsplane of zero lift normal to the axis of the rotor.
 11. Apparatus asclaimed in claim 7 wherein the body is rotationally symmetrical aboutits vertical axis and wherein at least three equiangularly arrangedconduits are provided.
 12. Apparatus as claimed in claim 7 wherein theturbine comprises a rotor having a plurality of blades each of which isof aerofoil cross-section and is fixed with its plane of zero liftnormal to the axis of the rotor.
 13. Apparatus as claimed in claim 9wherein the turbine comprises a rotor having a plurality of blades eachof which is of aerofoil cross-section and is fixed with its plane ofzero lift normal to the axis of the rotor.